Idk. Really depends on what you put there. And Nextcloud does file sync. Even if the server becomes unavailable, you'd still have your directories and calendar on your devices. Just collaborating and uploading stuff won't work.
And creativity and problem-solving are core scout skills, so I guess bulding that thing for no money would be an interesting exercise in that. Though you're right. At some point you'll have to think about maintainability and reliability. I guess that wouldn't stop me from starting the project, but everyone has to decide for themselves.
(And yes, a proper VPS would be a preferrable solution for a multitude of reasons.)